Hydrolysis of inulin



Patented Feb. I, 1927.

TED STATES PATENT orrlcs,

HW-ILL o. ARSEM, or SCHENECTADY, NEW Your; ASSIGNOR ro mnusram 'raorr-v mos oonromrron. or scnmmorany, NEW roan, 'A oonromrron or NEW YORK.

HYDBULYSIS: 0F INULIN.

No Drawing.

TlllS invention relates to an improved method of preparing fructose from inulin and to an improved product resulting from the application of thismethod in its preferred form.

The method of the present invention is applicable to inulin containing materials of any kind but preferably it is applied to clarified and purified inulin solutions obtained from the juice of the dah-lia bulb in accordance with the methods described in my copending applications, Serial No. 369,537 and Serial No. 424,459. When the improved method is applied in its preferred form to pure inulin, prepared according to these processes, the final fructose sugar product obtained is of unusual-purity and is especially suitable for consumption as a food and also possesses unusually good keeping qualities.

Many attempts have hitherto been made to prepare a low cost sugar in the form of syrup, crystals, powder or the like, which could be substituted for sucrose (i. e., beet or cane sugar) for certain important uses such as the preparation of soda syrups and soft drinks, the preservation of fruits, the manufacture of confectionery, for general cooking pur oses, for table use and similar purposes. ut these attempts havebeen at most only partially successful. The nonsucrose syrups prepared hitherto for commercial consumption, such as starch syrups, corn syrups, malt syrups and the like, and all the solid, powdered and partially crystalline products prepared from similar sources, have failed to meet the requirements which a sugar must have in order to compete in the market with'cane and beet sugar products for many important commercial purposes.

Thus, for example, none of theforegoing non-sucrose or sucrose substitute syrups are even approximately as sweet as the syrups prepared from cane or beet sugar. Also such syrups are usually highly colored and, therefore, cannot be used for many purposes for which ordinary refined cane or beet. sugar syrup is employed and furthermore, certain of these syrups possess peculiar or variable flavors which render them undesirable for many of the purposes mentioned. llhus in Application filed July 12,

the preparation of carbonated or soft drinks it is desirable that the syrup used shall. have a definite and uniform flavor. If the stock syrup or sugar from which'the soda-syrup is prepared has a peculiar or variable flavor of its own, it is not possible to prepare from it (by adding anatural. or artificial flavoring substance) a soda syrup having a flavor or taste of the desired definiteness or purity and uniformity. On the contrary in suchinstances the finished soda-syrup Wlll have "a mixed flavor and this will vary with the,

varying flavor of the stock syrup with which the natural or artificial flavoring material or extract is mixed to produce the finished soda-syrup.

Likewise in the production of confectlonery and culinary products uniformity and purity of. flavorof the finished product a are two of the most important requirements and therefore the sugar or syru used must not possess a variable flavor an preferably;

should not have a highly pronounced flavor of its own.

Furthermore, uniformit of color of all of.

the above mentioned finis ed products is an important additional requirement and for this reason stock syru s or sugars with a pronounced or. non-uni orm or objectionable erty of absorbing moisture. and becoming more or less pasty so that they-cannot be readily handled. Many of them also undergo objectionable decompositions, when the attempt is made to keep them in storage for any considerable length of time or when they are'emplo ed in cooking operations or in the manuactors of confectionery.

The product of the present invention tulfills all the foregoing re uirements to an extraordinary degree and oes not possess any of the above mentioned objectionable qualities and particularly it possesses the property of sweetness in much greater degree than even, cane or beet. sugar. It is almost, if not quite, astree-from objectionable c'olsugar syrup, so that it may-be employed for all the purposes for which ordinary wateris made necessary white cane sugar syrup is employed. F urthermore, in syrup form it may be cooked or boiled without discoloration. Also. in s 'rup form or in crystalline or solid form the fructose-sugar food-product .of the present invention is resistant toward the attack of certain objectionable molds 'andbacteria and therefore possesses good keeping qualities.

Because of the ready availability and cheapness of the raw materials used and the simplicity and economy of the method, by means of which'the finished product of the I present invention is produced, it can be manufactured at a very low cost.

The methods hitherto commonly employed for preparing pure fructose from inulin involve complicated and expensive methods of rte-crystallization, usually fromalcohol. Such recrystallization or other purification because the older methods of hydrolysis yield discolored products or products which contain hygroscopic, deleterious or otherwise objectionable impurities and which are therefore unsuited for many of the uses for which ordinary refined cane sugar products are em loyed. This is true even when highly puri ed inulin is used.

These impurities'a're very difficult to remove from the fructose by bleaching treatments, crystallization or similar methods and therefore to obtain the fructose in even an approximately pure form by these older methods, it has been necessary to repeat the purification treatments 21 great many times. The final yield of fructose so obtained is, therefore, so small that the cost of manufacturing by these older methods upon a commercial scale would be prohibitive.

The method of hydrolysis employed in producing the product of the present invention produces fructose of a high degree of purity directly from the inulin and thus avoids all the foregoing dificulties and disadvantages. It is based mainly upon a regulated hydrolysis of the inulin under definitely controlled conditions and in its preferred form the hydrolysis is carried out with a selected acid and also with a definite range of concentration of the acid. One of the most important features of the improved method referred to is the adjustment of the time of hydrolysis to varying concentrations of acid and to the varying chemical nature of the acid. It has been found that highly advantageous results are obtained by stopping the hydrolysis at the end of a definitely determined period of time. In determining this correct time of hydrolysis, account is taken, as already mentioned, not only of the chemical nature of the acid .but also of the concentration of the acid and also in certain instances of the temperature and pressure. By conduct-- ing the hydrolysis in this manner the inulin is readily hydrolyzed completely into fructose'of a very high degree of purity and a solution of pure fructose is obtained directly from the inulin solution without the necessity of resorting to the older elaborate and expensive methods of purification or crystallization previously mentioned. Moreover, the fructose is obtained directly in the form of a highly concentrated syrup and thus the cost of evaporatingthe solution is entirely avoided.

In other methods sometimes employed in the hydrolysis of inulin, a great deal of uncertainty has existed as to the optimum duration of the hydrolysis in order to obtain best yields of fructose. These uncertainties'in the older methods referred to are due in large part to the circumstance that the intermediate hydrolytic products of. inulin, as well as the decomposition products, resulting from various side reactions, all have properties which resemble those of fructose. If, therefore,

one selects any convenient property of fructose and attempts to determine the concentratlon of the fructose in the mixed solution by measurements of this property, the results obtained will represent the resultant value of this property for all of the substances present. Thus, for example, since many of the hydrolytic and decomposition products are optically active or possess the power to rotate the plane of polarized light, the, measurement of this property, as the hydrolysis progresses, does not always give a true measure of the concentratIon of fructose in the solution but corresponds to the resultant rotation of the mixture of all the optically active sub-' stances present. The measurement of the reducing power of the solution, as a means of following the progress of hydrolysis,

leads to similar confusing results for a similar reason, namely, that the various hydrolytic and decomposition products each has a characteristic reducing power of its own and, therefore, the reducing power of the mixed solution represents the resultant of that of all the substances present and cannot be used as a measure of the concentration of any single one of the products present.

It is, therefore, exceedingly difficult to determine just when the concentration of fructose in the mixed solution has reached a maximum value. I

In the method employed in the present invention as the hydrolysis of inulin progresses, the value of the negative rotation of polarized light, produced by the solution,

.usually increases at the beginning of the hydrolysis and then later decreases. In other methods this first maximum negative n trates value of rotation has frequently been taken to indicate the highest obtainable concentration of fructose inthe solution. l-have discovered, however, that this is not the case and that if the hydrolysis be continuedafter this first maximiim negative rotation is reached, the ne ative value of the rota.

1 tion again usually increases and passes through a second-maximum. Similarly several dillerent maximum values of negative rotation may be passed through during the course of the hydrolysis before the highest possible negative rotation is attained. Furthermore, I have found that when the hydrolinto fructose. In this calculation the specific rotation [111 of fructose is taken as minus ninety three degrees and the concentration of inulin in thesolution is calculated from' the weight of purified inulin dried to con- 7 stant weight at 90 (3., which was originally employed in makin up the solution. lln this calculation the ormula of inulin dried under these conditins is taken as 0 11 0 Fructose exists in two tautomeric' forms which areprobably stereoisomers, and are supposed to have the following formulaeonion on on onion o o HO-d-H no-d-n n-h-on H-dl-OH MA H t l HlOH HaOH The beta form, which is the ordinary crystalline form of fructose in the pure state has a theoretical rotation of minus 135.5 at 20.C.,-but when dissolved in water a portion of the beta form is supposed to change over into the alpha form, which has not been isolated as tar'as the applicant knows,

but has a calculated rotation of -21 at 20 40. The net effect after equilibrium is the percentage of inulin which is completely hydrolyzed to fructose and one hundred percent. l, have found that theseimpurities are objectionable because they interfere with the subse uent crystallization of fructose from solution and also because they impart increased hygroscopic properties to.

the solid fructose obtained by crystallization or by evaporation of" the hydrolyzed solution completely to dryness, in accordance with methods such as that described in my co-pending application, Serial No. 369,537. Moreover, in many instances certain of these impurities, particularly those formed by the decomposition of fructose afteuthe latter has been formed, produce objectionable discoloration of the solution and also discolor the solid fructose obtained.

therefrom. They also impart a variable or objectionable flavor to the product.

' Also-ll have found that there is an optimum concentration for. any given acid, by means of which substantially one hundred percent conversion of inulin tofructose can we obtained. A greater or smaller concentration than this optimum concentration,

gives a poorer result. It has now been found that to obtain a maximum conversion with a strong inorganic acid requires a greater optimum concentration of acid than with an organic acid. Thus, for example, the

optimum concentration for hydrochloric acid is approximately five hundredths normal, while with acetic acid the optimum concentration is only about six .thousandths normal. With hydrochloric acid of this optimum concentration, the maximum conversion of inulin to fructose is reached in about five to ten minutes, whereas with acetic acid, of the above given optimum concentration, eight hours are required to produce a maximum conversion of the inulin to fructose.

Furthermore, l have discovered that thetime required to reach a maximum conversion with any given acid bears a certain definite and fixed relation to the concentration of the acid and'that for each kind of acid, keeping theinulin concentration constant, this optimum time required for maximum conversion increases as the concen tration of the acid diminishes, in such a way that the logarithm of the reciprocal of the time is approximately proportional to the logarithm of the normal concentration of the acid. In other words, the acid strength plotted against the reciprocal of the correspondin time gives an aproximately straight line on logarithmic paper. A different line is obtained, of course. for each kind of acid. Furthermore, I have discovered that the results obtained with car tam orgamc aclds such as acetic, citric will .0075 and .03. between concentration and time holds good centration o ner, give straight lines which are approximately parallel and which lie relatively close together. In other words, I have discovered that for different acids belonging to this general class, approximately the same quantitative relationship exists between different Log. N=a log. %,+log. 'b.

In which N represents the normality of the acid in the usual sense, assuming that onl the first hydrogen ion of the acid is active, while T is the time required for the highest possibleyield, expressed in hours and inwhich the constant a has a value between about .7 and 1 and the constant b' has a value varying between about The foregoing relationship for temperatures between about C. and 120 C. and for pressures of about one atmosphere. This relationship is not seriously affected b changes in the original conthe inulin solution for concentrations greater than about eight percent by weight.

While it 1s desired that the scope of the presentinvention shall not be restricted by any unproven assumptions as to the exact chemical nature of the reactions produced during the hydrolysis by certain organic acids such, as acetic, citric maleic, malic, fumaric, lactic and tartaric acids on the one hand and b inorganic acids such as hydrochloric aci on the other hand, nevertheless, it is believed that the wide diiference in their action may be best ex lained in the following manner. thought, acts as a catalyst in the hydrolysis of inulin by virtue of the hydro en ion concntration, while the failure 0 any given acid to produce a one hundred percent conversion under certain conditions or with certain concentrations is believed to be due to a condensing action of the undissociated molecules of the acid or of the anion upon the products of the hydrolysis of inulin and particularly upon the fructose. In other words, at each stage of the hydrolysis there seems to 'be two reactions going on which are opposed to each other in their effects, one reaction producing hydrolysis ofinulin, probably through several intermediate stages, and" another reaction bring-v ing about a decom osition or a condensation of the different by rolytic products and particularly offructose. I believe that there are three principal stages in the hydrolysis of inulin and that The aci it istwo principal intermediate hydrolytio products are formed before .fructose is produced, thus balm-compound" #1-compound #2fructose The reasorgirccording to my belief that the final stage has never hitherto been completely attained, is that the hydrolysis has been conducted under such conditions that the acid destroys the fructose or the intermediate compounds forming hygroscopic substance such as le'vulosin,- and also other decomposition products such as humin, levulinic acid, formic acid, etc. It is my belief also'that the several different maxlma of polarization already described, which are obtained during the course of the hydrolysis, correspond to maximum concentrations ,of these principal intermediate hydrolytic compounds and I am convinced that this is the reason that the significance of these different maxima has hitherto been misunderstood resulting in a failure to obtain purefructose' directly from inulin as in the improved method of the present invention.

An example of my preferred method of carryingout the hydrolysis of inulin is as the tartaric acid functions as a mono-basicacid, only the first H ion being active. Specifically, I may take 100 kilograms of inulin cake obtained by filterpressing or otherwise, containing 30-60% anhydrous inulin as determined by drying to constant weight at 90 C. This is put into an acid-proof vessel provided with an agitator and means for heating and is heated to 100 C. with continuous stirring, whereupon it assumes a thin creamy consistency. Tartaric acid, 75 gms. dissolved in a small amount of water, say one litre, is now added and the heating continued for between" two and three hours, or until approximately 100% of the inulin has been converted into fructose as determined by polariscopic tests as previously described. The resulting product is a practically pure concentrated syrupy solution of, fructose. A smaller or larger amount of tartaric acid can be used with a corresponding change in the me as previously specified. The syrup may be used as such or evaporated or crystallized as for example as described in my co-pendin applications Serial No. 369,537 and Seria No. 424,459.

It will be understood that I, do not rerename and conditions described in the preceding example, but I may alter or vary these in accordance with the general characteristics and features of my invention as previously described. v

Among the principal advantages of the improved fructose food-product of the pres ent invention, as compared with similar products hitherto known, are its greater stability especially toward heat, its exceptionally good keeping qualities, and in solid or crystalline form its greater freedom from a tendency to cake or become pasty when exposed to a moist or humid atmosphere. These special advantages of the new product particularly its greater stability toward heat and its improved keeping qualities are due in large part, I believe, to the unusual purity of the product andto the nature and degree of its acidity. In some instances (and particularly where good keeping qualities are especially desired) I have found that these advantageous properties can be increased by first hydrolyzing the pure inulin with the limited amount of acid as specitied and then, afterthe hydrolysis is com pleted and the product has cooled, adding an additional amount of acid either to the syrup or to the solid, or crystalline product obtained therefrom by evaporation or crystallization as, for example, by the method of evaporation and crystallization described in my co-pending' a plications, Serial. No. 369,537 and Serial 0. 424,459. 'Where the product is intended for consumption as a food itself or as a constituent of a food, I prefer to add an innocuous or edible acid such as citric acid and preferably tartaric acid or an acid tartrate or the like.

In the manufacture of candy or confectionery and in many culinary operations where a sugar is employed, it is highly desirable that the sugar shall not decompose or darken in color when cooked or heated and the improved pure fructose food-product of the present invention meets these requirements in a much more satisfactory manner than any similar product hitherto known. 3

When a pure fructose syrup, prepared according to my invention, is allowed to stand for several days, it sometimes becomes slightly cloudy, which is objectionable, and I have found that this cloudiness is due to the formation of a small amount of calcium tartrate. The calcium comes from minute traces of compounds of this metal which sometimes remain in the clarified inulincontaining juices after clarification, unless special care is taken to remove these last traces of calcium in some convenient manner. If tartaric acid is used for hydrolysis this difficulty can be overcome by filtering the syrup before bottling it, after it has been stored for a few days. A still better method of avoiding this difficulty is to carry out the hydrolysis by means of an organic acid which forms calcium salt more soluble than calcium tartrate, such as lactic, maleic, malic, or fumaric acid.

The claims of the present application relate to the herein described method of converting inulin into fructose. In a divisional application Serial No.; 516,866, I have claimed the fructose product disclosed herein; in a divisional application No. 731,967, I have claimed a method of recovering the fructose produced from the solution of inulin in which an organic acid is employed to obtain the desired hydrogen ion concentration of the solution; and in a divisional application Serial No. 731,966, I have claimed a method of recovering the fructose produced from the solution of inulin in which an inorganic acid is employed to obtain the desired hydrogen ion concentration of the solution.

I claim: 1. The method of converting inulin t fructose which comprises subjecting a solution containing inulin to the action of an acidpresent in the solution in any desired concentration, continuing the action of the acid until the rotation of polarized light produced by the solution passes through a maximum decreases and again increases to a further and higher maximum than that first obtained.

2. The method of converting inulin to fructose which comprises subjecting a solution containing inulin to the action of an acid present in the solution in any selected concentration and continuing the action of the acid until a sample of solution at ordinary temperature produces a rotation of polarized light corresponding to a calculated specific rotation for fructose of about [a] :-93, calculated upon the basis that the inulin is converted entirely into fructose and that the formula of pure inulin is C II O when dried to constant weight at 90 C., substantially as described.

. 3. The method of converting inulin to fructose which comprises subjecting a solution containing inulin to the action of an organic acid present in the solution in any desired concentration and continuing the action of the acid for a period of time such that the logarithm of the normality of the acid with respect to the first replaceable hydrogen ion thereof is about equal to the product of a constant varying from 0.7 to 1 and the logarithm of the time expressed in hours plus the logarithm of a constant between .0075 and .003.

4. The method. of converting inulin to fructose which comprises subjecting a solution containing inulin to the action of an organic acid present in the solution in a concentration of from'about five thousandths to fifteen thousandths normal with respect to the first replaceable hydrogen ion thereof and continuing the action of the acid for a period of time such that the logarithm of the hydrogen ion concentration expressed in equivalents is equal to ,the product of a constant varying from 0.7 to 1 and the logarithm of the time expressed in hours plus the logarithm of a constant between .0075 and .003.

5. The method of converting inulin to fructose which comprises subjecting a solution containing inulin to the action of an organic acid present in the solution in a concentration of from about five thousandths to fifteen thousandths normal with respect to the first replaceable hydrogen ion thereof for a period of from about two to three hours.

6. The method of converting inulin to fructose which comprises subjecting a solution containing inulin to the action of tartaric acid present in the solution in a concentration of from about five thousandths to fifteen thousandths normal with respect to the first replaceable hydrogen ion thereof for a period of from about two to three hours.

7. The method of converting inulin to fructose which comprises subjecting a solution containing inulin to the action of tartaric acid present in the solution ina concentration of from about five thousandths to fifteen thousandths normal with respect to the first replaceable hydrogen ion thereof at a temperature, of from about 70? C. to

100 C. for a period of from about two to three hours, the solution being maintained under a pressure of about one atmosphere.

8. The method of converting inulin to fructose which comprises subjecting a solution containing inulin to the action of an acid present in the solution in any desired concentration, continuing the action of the acid until the solution produces a maximum rotation of polarized light and the rota tion begins to decrease and then continuing the action until further maxima are reached terminating the reaction'- at the highest attainable rotation of polarized light.

9. The method of converting inulin to frnctosewhich comprises subjecting a solution containing inulin to the action of an acid present in the solution in any desired concentration, permitting the reaction to continue until the rotation of polarized light produced by the solution goes through a maximum and begins to decrease and continuing the reaction until a further maximum rotation of 93 at is attained.

,10. The method of converting inulin to fructose Which comprises subjecting a solution containing inulin in a concentration greater than about to the action of an organic acid present in the solution in a concentration of from about five thousandths (.005) to fifteen thousandths (.015) normality with respect to the first replaceable hydrogen ion thereof for a period of from about two to three hours.

In testimony whereof I affix my signature.

WILLIAM C. ARSEM. 

